An organic electroluminescence device is a self-luminous luminescence device. Since the research and development teams of Kodak and Cambridge discovered the organic electroluminescence device from 1987, improving the luminous efficiency of the organic electroluminescence device has always been one of primary focus for research and development. The organic electroluminescence device has a relative high contrast ratio in a dark room. However, in a regular daily environment, the contrast ratio is deteriorated due to the organic electroluminescence device is most likely utilized with a metal electrode capable of reflecting ambient light.
The maximum contrast ratio (CRmax) of a display is the ratio (that is, Lmax/Lmin) between the luminance (Lmax) of the brightest state and the luminance (Lmin) of the darkest state. Currently, the contrast ratio of commercially available liquid crystal displays may easily reach tens of thousands or even higher. Nevertheless, the luminance (Lmax) of the brightest state and the luminance (Lmin) of the darkest state described above are both measured in the dark room, it will be difficult to reach such high contrast ratio in a general operation environment. In practice, most of the contrast ratio that the display may present in the regular daily environment is less than the maximum contrast ratio (CRmax). For instance, the contrast ratio of the screen in a living room is different from the contrast ratio of the screen in a cinema. The difference between the contrast ratios arises from the influence of ambient light.
In the actual operation environment, the calculation of contrast ratio usually needs to consider an amount of ambient light (Ram) that is reflected by the display to the eyes of the user. The amount of light (Ram) relates to the reflectivity (Rsf) of the layers in the display and the intensity (Iam) of ambient light. In other words, the amount of light (Ram) is equal to the product (Rsf·Iam) of the reflectivity (Rsf) and the intensity (Iam) of ambient light. Thus, the actual contrast ratio (CR) of a display may be represented by the following equation (1):CR=(Lmax+Ram/Lmin+Ram)  (1)
The metal electrode of an organic electroluminescence display may reflect ambient light, and therefore, the organic electroluminescence display panel easily reflects an ambient image to human eyes. The reflected ambient image overlaps with an image intended to be displayed by the panel, such that the display quality of the organic electroluminescence display may be deteriorated.
In view of the above, to improve the brightness of an organic electroluminescence display and to block the ambient light that reflected by its metal electrodes has become one of the research topics to people having ordinary skill in the pertinent field.